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IS INTELLIGENCE INHERITED CONTOVERSY

Nature vs. Nurture - World Psychiatry. 2005 February; 4(1): 3–8. World Psychiatric AssociationAre genes destiny? Have adenine, cytosine, guanine and thymine replaced Lachesis, Clotho and Atropos as the weavers of our fate?
LEON EISENBERG11Department of Social Medicine, Harvard Medical School, 641 Huntington Avenue, Boston, MA 02115-6019, USA Abstract
It is as futile to ask how much of the phenotype of an organism is due to nature and how much to its nurture as it is to determine how much of the area of a rectangle is due to its length and how much to its height. Phenotype and area are joint products. The spectacular success of genomics, unfortunately, threatens to re-awaken belief in genes as the principal determinants of human behavior. This paper develops the thesis that gene expression is modified by environmental inputs and that the impact of the environment on a given organism is modified by its genome. Genes set the boundaries of the possible; environments parse out the actual.
Keywords: Genomics, ontogenetic niche, polyphenism, collective efficacy, heritability, phenylketonuria, thalassemia, gene regulation, Williams syndrome
When I completed my psychiatric training in the United States, more than a half century ago, genetics was anathema. Psychoanalysis was viewed as the cutting edge of psychiatry and excited the best and the brightest of young residents.
Fifty years later, psychiatry in the United States has been turned upside down. The discovery of psychotropic drugs has transmuted psychiatrists into psychopharmacologists. Despite extensive evidence that manualized psychotherapies (cognitive behavior therapy and interpersonal psychotherapy) are as effective as tricyclics and selective serotonin reuptake inhibitors for mild and moderate depression, interest in psychological treatments continues to wane.
Prodigious advances in neuroscience and in brain imaging have yielded a dynamic model of a brain that is shaped by experience and continues to change over the life course. To cap the revolution, the mapping of the human genome promises to make it possible to identify genes that influence risk and resistance to psychiatric disorders. Discoveries in neuroscience and genomics continue the reshaping of psychiatry into a disproportionately biological specialty where it had once been a disproportionately psychosocial specialty.
Despite the one-sidedness, the gains in our science base constitute a very considerable advance over the days when I was trained. What is unacceptable in the "new" psychiatry is a naïve genetic determinism that fails to take social context into account, just as the "old" psychiatry ignored biology. Just as I was troubled by psychoanalytic exclusivism then (brainless psychiatry), I am troubled by the dominance of a fixation on biology (mindless psychiatry) that ignores social context (1). The aim of this paper is to reiterate the central principle of evolutionary genetics: just as the unique response of the organism to its environment depends on its genome, the expression of that genome is conditioned by that environment. <snip>

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Here we demonstrate that the trajectory of change in the thickness of the cerebral cortex, rather than cortical thickness itself, is most closely related to level of intelligence.
Using a longitudinal design, we find a marked developmental shift from a predominantly negative correlation between intelligence and cortical thickness in early childhood to a positive correlation in late childhood and beyond. Additionally, level of intelligence is associated with the trajectory of cortical development, primarily in frontal regions implicated in the maturation of intelligent activity.
More intelligent children demonstrate a particularly plastic cortex, with an initial accelerated and prolonged phase of cortical increase, which yields to equally vigorous cortical thinning by early adolescence. This study indicates that the neuroanatomical expression of intelligence in children is dynamic.

Intelligence, Race, and Genetics
Robert J. Sternberg, Elena L. Grigorenko, and Kenneth K. Kidd: Yale University January 2005 - American Psychologist: Vol. 60, No. 1, 4659 http://www.apa.org/journals/releases/amp60146.pdf
Abstract: In this article, the authors argue that the overwhelming portion of the literature on intelligence, race, and genetics is based on folk taxonomies rather than scientific analysis. They suggest that because theorists of intelligence disagree as to what it is, any consideration of its relationships to other constructs must be tentative at best. They further argue that race is a social construction with no scientific definition. Thus, studies of the relationship between race and other constructs may serve social ends but cannot serve scientific ends. No gene has yet been conclusively linked to intelligence, so attempts to provide a compelling genetic link of race to intelligence are not feasible at this time. The authors also show that heritability, a behaviorgenetic concept, is inadequate in regard to providing such a link.

Conclusion
In conclusion, intelligence is, at this time, ill defined. Although many investigators study IQ or g as an operational definition of intelligence, these operationalizations are at best incomplete, even according to those who accept the constructs as useful (e.g., Carroll, 1993).
Research suggests that properties of intelligence beyond g may be somewhat different from those of
g (e.g., Gardner, 1983; Sternberg et al., 2000, 2001). Race is a social construction, not a biological construct, and studies currently indicating alleged genetic bases of racial differences in intelligence fail to make their point even for these socialdefined groups. In general, we need to be careful, in psychological research, to distinguish our folk conceptions of constructs from the constructs themselves.

intelligence, inherited, race, genetics, intelligence research

Dr Paul Thompson, from the University of California at Los Angeles, compared 20 twin pairs, half of whom were identical and half Non-identical. Fiindings showed genetic factors accounted for differences between individuals in key areas such as intelligence and language ability.Identical twins have the same genes, whereas non-identical twins, like ordinary siblings, share about half. Features which are the same in identical, but not non-identical twins are therefore likely to be governed by genetic factors.

"We found that brain structure is under significant genetic control, in a broad anatomical region that includes frontal and language-related cortices.
"The quantity of frontal grey matter, in particular, was most similar in individuals who were genetically alike; intriguingly, these individual differences in brain structure were tightly linked with individual differences in IQ."
"The resulting genetic brain maps reveal a strong relationship between genes, brain structure and behaviour, suggesting that highly heritable aspects of brain structure may be fundamental in determining individual differences in cognition."

evidence that intelligence is largely determined before birth from a new genetic study of twins.

Grey matter volume - a measure of the density of brain cells - was strongly determined by genes, and reflected cognitive performance.

Studies suggest many cognitive skills are surprisingly
heritable.

Strong genetic influences on IQ, verbal and spatial abilities, perceptual speed, and even some personality traits including
emotional reactions to stress.

UCLA brain mapping researchers have created the first images to show how an individual's genes influence their brain structure and intelligence.

The findings, published in the Nov. 5 issue of the journal Nature Neuroscience, offer exciting new insight about how parents pass on personality traits and cognitive abilities, and how brain diseases run in families.

The team found that the amount of gray matter in the frontal parts of the brain is determined by the genetic make-up of an individual's parents, and strongly correlates with that individual's cognitive ability, as measured by intelligence test scores.

More importantly, these are the first images to uncover how normal genetic differences influence brain structure and intelligence.

Brain regions controlling language and reading skills were virtually identical in identical twins, who share exactly the same genes, while siblings showed only 60 percent of the normal brain differences.

This tight structural similarity in the brains of family members helps explain why brain diseases, including schizophrenia and some types of dementia, run in families.

“We were stunned to see that the amount of gray matter in frontal brain regions was strongly inherited, and also predicted an individual's IQ score,” said Paul Thompson, the study's chief investigator and an assistant professor of neurology at the UCLA Laboratory of Neuro Imaging.

“The brain's language areas were also extremely similar in family members. Brain regions that were found to be most similar in family members may be especially vulnerable to diseases that run in families, including some forms of psychosis and dementia.”

The scientists employed magnetic resonance imaging technology to scan a group of 20 identical twins, whose genes are identical, and 20 same-sex fraternal twins, who share half their genes.

Using a high-speed supercomputer, they created color-coded images showing which parts of the brain are determined by our genetic make-up, and which are more adaptable to environmental factors, such as learning and stress.

To create the maps of genetic influences on the brain, the UCLA scientists teamed up with the National Public Health Institute of Finland, and the Finnish Universities of Helsinki and Oulu.

In a national initiative, the Finnish team tracked all the same-sex twins born in Finland between 1940 and 1957 — 9,500 pairs of twins — many of whom received brain scans and cognitive tests.

Their genetic similarity was confirmed by analyzing 78 different genetic markers. These individual pieces of DNA match exactly in identical twins, and half of them match in siblings.

Recent research has shown that many cognitive skills are surprisingly heritable, with strong genetic influences on verbal and spatial abilities, reaction times, and even some personality qualities, including emotional reactions to stress.

These genetic relationships persist even after statistical adjustments are made for shared family environments, which tend to make members of the same family more similar. Until this study, little was known about how much individual genotype accounts for the wide variations among individual brains, as well as individual's cognitive ability.

The UCLA researchers are also applying this new genetic brain mapping approach to relatives of schizophrenic patients, and individuals at genetic risk for Alzheimer's disease, to screen them for early brain changes, and help understand familial risk for inherited brain disorders where specific risk genes are unknown.

Study Finds Genetic Link Between Intelligence and Size of Some Regions of the BrainBy NICHOLAS WADE - NEW YORK TIMES November 5, 2001 http://www.nytimes.com/2001/11/05/health/anatomy/05BRAI.html

Plunging into the roiled waters of human intelligence and its heritability, brain scientists say they have found that the size of certain regions of the brain is under tight genetic control and that the larger these regions are the higher is intelligence.
The finding is true only on average and cannot be used to assess an individual's intelligence, said Dr. Paul M. Thompson, the leader of the research team and a pioneer in mapping the structure of the brain.
The measurement of intelligence has long been a controversial issue, and even more so the efforts to tease out the relative contributions of heredity and environment.
Dr. Bruce L. Miller, a neurologist at the University of California at San Francisco and an expert on brain changes in Alzheimer's disease, said Dr. Thompson's work was "an exciting study that starts to show there are some brain areas in which there are very significant genetic influences on structure."
And Dr. Robert Plomin, a psychologist who studies intelligence at the Institute of Psychiatry in London, said the high correlation found between the size of certain areas of the brain and general intelligence "does make it harder to dismiss intelligence as some meaningless construct, as some want to do."

Independent Grey matter does influence intelligence, say scientistsBy Steve Connor, Science Editor
05 November 2001
Scientists have for the first time linked the amount of grey matter in the brain with the ability to do well in intelligence tests. The study, confirming that grey matter really was the intellectual stuffing of the brain, also found that the amount a person had depended largely on genes. The findings emerged from a study of identical and non-identical twins who had their heads examined using a medical scanner that could distinguish between the brain's grey matter and the rest of its "white matter".
Grey matter ­ so called because it looks grey to the naked eye ­ is made of the central "cell bodies" of brain cells and has long been associated with intelligence despite there being little evidence to justify the link. White matter, however, is made up of the long filaments that extend from nerve cells and act as the electrically insulated "cables" transmitting messages over longer distances.